C4 Vibration problem

I have a 1988 covertible, L98, with 4+3 tranny. Occasionally at highway speeds I will get a heavy vibration. It fells like I have a tire going flat. It doesn't pull to either side, just the rumbling.
It may last for 1/2 mile or for 2 miles, but it eventually goes away. Any ideas??
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Possibly a u-joint replacement is needed?

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Have someone stand outside the car and go from forward to reverse rolling 3 or 4 ft each way to listen for any noise... Sounds like you got some needle bearings in the U joints chewed up. And it sets up a wobble from time to time. Could also be a torn up rear wheel bearing assembly on the trailing arm.. the forward/reverse generally will produce some noise also. Jack up the front and see if you can get the wheel to move from bottom to top checking for frt wheel bearing slop.
If it was tranny or differential I'd think it would be consistent.
Does the vibration seem to be felt in your seat or the steering wheel? Or just throughout the whole car?
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snipped-for-privacy@inxpress.net wrote:

it was after I hit certain bumps in the road. The car would pickup a vibration (almost like a tire out of balance) and then fade away. I took it to my mechanic and they went over and over the car and couldn't find anything wrong they balanced the tires and did a 4 wheel alignment but nothing seemed to work (they only charged for the alignment and then only 1/2 price since it didn't actually fix anything). Sometime later I had to replace the tires (for another reason) and I mentioned the problem to the tire guys (different shop, the main shop I use doesn't actually do tire sales and get the tires from the other guy if someone wants to order tires) and they said that was not uncommon for the Goodyear tires I was running when they get old. Sure enough after the new tires went on the problem had gone with the old tires.
Dennis.
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wrote:

How many miles on the car, & tires? How common is it for old tires and not just Goodyear? New soft rubber of most any brand feels better sometimes as long as the previous tires felt good. Sounds like dealer speak to me.
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Dad
05 C6 Silver/Red 6spd Z51
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Dad wrote:

distance (like if you have ever had really soft racing tires that get flat spots and need to be warmed up) and only happened after hitting certain bumps in the road. The problem went TOTALLY away after the new tires. BTW... That was not the only set of tires (same series Goodyears) that did that either.
Dennis
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I understand that, so what you're saying is that it is only old Goodyear tires and not the type of vehicle or worn/weak suspension? The different set of Goodyear's didn't do it until they got old, right? So you're now saying that the new tires won't do that even when they get old, or they never will? Not saying what is said about the Goodyear tires is wrong, just that it may have something to do with other things besides tires. My guess is that a new set of Goodyear's would have taken the problem TOTALLY away also. Again, it would help to make a more informed decision on buying tires if we knew what kind of mileage and how old the Goodyear's were. By the way that's how my '92 LT1 Flexible Flyer felt most of the time but then I only had 92K on it and 3 different sets of tires. First and last set were Goodyear's and the set in the middle were Michelin, worst of the lot.
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Dad wrote:

--like maybe an out of balance shake but sometimes faster ?? Feels like running over a mile-long line of little, closely spaced lumps in the road -- or small lumps in the tread ?
I had that with a set of IRI tires on the 911. (quiet tire with a nylon belt overlaying the steel.) Would come and go at different speeds, tire temps etc. Changed shock settings-- problem went away then came back 500 miles later--changed both rear shocks problem stayed away-- shock bushings were chewed up. ...PJ
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Not really, just pointing out the accepted weak structural design of the C4. It totally went away when I traded for the C5.

Never had that with the C4, just the sloppy frame that shook after a bump. Alignment and balance were well tended with even tire wear and replaced them with 35 and 40k on them.
How many miles were on the Goodyear's you were referring to? How old were they?
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Dad
05 C6 Silver/Red 6spd Z51
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Dad wrote:

brace or a loose top. My 911 though was a pretty rigid critter. Possibly not as stiff as the C6 but comparable to the C5s I've driven. ....PJ
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You seem to be avoiding the question about the age and mileage of the Goodyear tires? Now where did the comparison of the C6/C5 come from? Time for me to drop this thread, you have no intention of answering the question that back up your statement about Goodyear tires.
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Dad wrote:

Sorry about dictating road map info to a higher authority. {{{ ;-)
.... PJ
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You seem to confuse easily... How could PJ answer the question regarding mileage on MY car or tires??
For the first set of tires the car had about 60,000 miles but I'm not sure about the tires because I bought the car used and those were the tires that were on it. The second set had about 35,000 miles on them and were about 4 years old, the car had about 95,000 miles on it at that time. The current set of tires have close to 30,000 with no sign of doing this (this set is the newer "replacement" series) and maybe they won't do it. The tire shop was not referencing Goodyears doing that in general, but that the specific model Goodyear I was using did that.
One difference is that on the first set I felt it much more in the steering like it was the front tires and on the second set it felt more in the rear.
Since I have owned the car, it has had nothing but Goodyear tires on it, so I have no reference to any other tire for the Corvette. I strictly run Michelin Pilots on my IROC Camaro (only get about 10,000 miles per set, but they stick real well) and on previous performance cars I was using BF Goodrich and Hoosers grooved for the street (not totally legal).
I have experienced frame flex on other cars and this was not that. I have never had frame flex keep going for a mile or two after the bump. I don't it was shocks or anything on the suspension, Two different shops check it over very closely and did not find anything (as I said before, one shop looked at it for two days).
BTW... I'm not new to car mechanics. Not only have I built numerous cars and had two cars in Car Craft and Hot Rod mags. I currently am an engineer working on a Champ Car Atlantic team.
Dennis
Dad wrote:

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Not confused, just wanted him to answer the questions he was presenting about someone elses car and tires. He couldn't or won't, just shot off into another direction.

Were they the same size front and rear?

Not saying it was just frame flex but a combination of tire age, and miles on a frame that flexes. Back in the '70 when I was running Camaros with radials the '72 with reinforcing rails handled much better that the stock '74 without (no shutter coming out of hard corners), but then it was heavier also, both flexed less then the '92 Corvette. My '63 Corvette was a pig on the road but it took less than 2 hours for a good frame shop to find a frame and axel location problem after it had been to 3 other shops and inspected by a GM zone manager, (whatever that means).

Not suggesting that you were, just wanted PJ to back up what he was trying to get across to the readers. Never got an answer from him just more information about unrelated matters.
Let us know what you find if you would, good luck.
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Dad
05 C6 Silver/Red 6spd Z51
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Dad wrote:

uni-directional and of different sizes. The rims too are different sizes.

the results.
Dennis
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I knew there were 16 and 17 inch wheels but thought they were still mounted in sets of 4, size was dependant on the option. Are you wheeled and tired with something other than a normal setup for the '88?
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Dad wrote:

don't remember off the top of my head what the widths are, I can check if you're interested.
Dennis
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had a 75 that I couldn't seem to get balanced correctly. wasn't the tires. it needed the tires spin-balanced while on the car. (balances tire, rotor and all) its just hard to find someone that still does that.
my2
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